Method to produce flexible ceramic thermal protection system resistant to high aeroacoustic noise

ABSTRACT

A method of producing a three dimensional angle interlock ceramic fiber which is stable to high aeroacoustic noise of about 170 decibels and to high temperatures of about 2500 degrees F. is disclosed. The method uses multiple separate strands of a ceramic fiber or ceramic tow suitable for weaving having multiple warp fibers and multiple fill fibers woven with a modified fly-shuttle loom or rapier shuttleless loom which has nip rolls, a modified fabric advancement mechanism and at least eight harnesses in connection with a Dobby pattern chain utilizing sufficient heddles for each warp fiber and a reed which accommodates at least 168 ends per inch. The method produces a multilayered top fabric, rib fabric and single-layered bottom fabric.

ORIGIN OF THE INVENTION

The invention disclosed herein was made in the performance of work undera NASA contract and is subject to Public Law 96-517 (35 U.S.C. § 200 etseq.). The contractor has elected to not retain title in this invention.

This is a division of application Ser. No. 08/085,387, filed Jul. 1,1993 U.S. Pat. No. 5,451,448.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method to produce flexible ceramicthermal protection system (TPS) capable of surviving exposure to a highaeroacoustic noise level (170 decibel or greater) under fluctuating airloads, high temperature, and dynamic pressure conditions without the useor necessity of a surface coating to toughen the surface to theaeroacoustic load. The TPS is produced by having an integrally wovenceramic core structure filled with a ceramic insulation possessing hightemperature stability and low thermal conductivity insulationproperties.

2. Description of Related Art

Conventional ceramic insulation blankets are usually assembled in asandwich-like construction in which a layer of ceramic insulation isplaced between a single-ply top or face fabric and a bottom single-plyfabric and held together with a ceramic sewing thread in a quiltedstitch pattern. Sewn blankets can use other ceramic fabrics besidessilica. Another blanket configuration utilizes an integrally wovensingle-ply core structure filled with insulation. This thermal blanketis reported in the literature as Tailorable Advanced Blanket Insulation(TABI).

Disadvantages of Prior Art--The stitched blanket (held together with asewing thread) can fail during exposure to fluctuating pressures andhigh aeroacoustic loads, e.g. 170 decibels and a dynamic pressure of 510pounds per square foot (psf). This failure occurs after exposure to aradiant heat source as low as 10 minutes (min) at 1200° F. In somecases, the thread or threads start breaking within one min and canpropagate into fraying or tearing the surface fabric causing rapiddestruction of the surface fabric followed by removal or loss of theinsulation material. This loss renders the thermal insulation blanketuseless for its intended purpose.

A single ply woven TABI, which utilizes an integral weave structurewoven from 1800 denier silicon carbide yarn, when filled with silicabatting will quickly show fabric fraying as well as movement of theinsulation in the core or cell of the TABI structure. This occurs as lowas 10 min at 1440° F. exposure to a radiant heat source and similarsound pressure levels and dynamic pressures as the sewn, quiltedblankets.

This destructive result limits both these thermal blankets to lowaeroacoustic and low temperature applications thereby minimizing theadvantage of flexible ceramic blankets for applications, particularly insituations where acoustic resistance is required without resorting to orrequiring a surface ceramic coating to toughen the surface fabric. Thesecoatings can also degrade or interact with the ceramic fabric when curedat or exposed to high temperatures. The coating also adds weight.

Some art of interest is:

S. R. Riccitiello, et al. in U.S. Pat. No. 4,713,275 disclose a rigidceramic reusable externally applied thermal protection system.

A. R. Campman, et al. in U.S. Pat. No. 4,922,969 disclose a multilayerwoven fabric having varying material composition through its thickness.

D. A. Kourtides, et al. in U.S. Pat. No. 5,038,693 disclose compositeflexible multilayer insulation systems consisting of alternating layersof metal foil and ceramic scrim cloth or vacuum metallized polymericfilms quilted together using a ceramic thread.

H. Goldstein et al., "improved Thermal Protection System for the SpaceShuttle Orbiter." AIAA Paper 82-0630, May 1982.

B. Trujillo, et al., "In-Flight Load Testing of Advanced Shuttle ThermalProtection Systems." AIAA Paper 83-2704, November 1983.

P. M. Sawko, et al., "Effect of Processing Treatments of Strength ofSilica Thread for Quilted Ceramic Insulation on Space Shuttle." SAMPEQuarterly, Vol. 6, No. 4, July 1985, pp. 17-12.

P. M. Sawko, et al., "Performance of Uncoated AFRSI Blankets duringMultiple Space Shuttle Flights." NASA Technical Memorandum 103892,April, 1992.

D. Mui, et al., "Development of a Protective Ceramic Coating for ShuttleOrbiter Advanced Flexible Reusable Surface Insulation (AFRSI)." CeramicEng. and Sci. Proc., Vol. 6, No. 7-8, July-August 1985, pp. 793-805.

P. M. Sawko, "Flexible Thermal Protection Materials." NASA CP-2315,1983, pp. 179-183.

P. M. Sawko, "Tailored Advanced Blanket Insulation (TABI)." NASACP-3001, 1987, pp. 135-152.

D. P. Calamito, "Tailorable Advanced Blanket Insulation UsingAluminoborosilicate and Alumina Batting," Final Report. NASA CR-177527,July 1989.

C. F. Coe, "An Assessment of Wind Tunnel Test Data on Flexible ThermalProtection Materials and Results of New Fatigue Tests of Threads," FinalReport. NASA CR 177466, April 1985.

C. F. Coe, "An Investigation of the Causes of Failure of FlexibleThermal Protection Materials in an Aerodynamic Environment," FinalReport, NASA CR-166624, March 1987.

H. K. Larson, et al., "Space Shuttle Orbiter Thermal Protection MaterialDevelopment and Testing," Proceedings of 4th Aerospace Testing Seminar,1978, pp. 189-193.

P. M. Sawko, et al., "Development of a Silicon Carbide Sewing Thread."SAMPE Quarterly, Vol. 20, No. 4, July 1989, pp. 3-8.

P. M. Sawko, et al., "Strength and Flexibility Properties of AdvancedCeramic Fabrics." SAMPE Quarterly, Vol. 17, No. 1, October 1985.

H. K. Tran, et al., "Thermal Degradation Study of Silicon CarbideThreads Developed for Advanced Thermal Protection Systems." NASATechnical Memorandum 103952, August 1992.

None of these references individually or collectively teach or suggestthe present invention.

All articles, publications, books, journals, patents and patentapplications and the like are incorporated by reference in theirentirety.

What is needed is an integrated design and identification of materialswhich produce a flexible ceramic thermal protection system which hasimproved mechanical, thermal and sonic properties to high aeroacousticnoise (i.e. preferably about 2000° F., about 2300° or 2400° F. for 10min, or 2500° F. for 5 min). The present invention accomplishes theseobjectives.

Advantages of Invention of Prior Art

Some advantages over prior art include:

a. providing a ceramic blanket that can survive exposure to highaeroacoustic noise levels (170 decibels) after exposure to 2500° F.radiant heat.

b. providing a TPS that eliminates the need of a ceramic surface coatingto improve the aeroacoustic performance of flexible ceramic TPS blanketsafter exposure to high temperatures.

c. providing a low density TPS for a savings in weight.

d. providing a flat, smooth surface for aerodynamic smoothness ascompared to bumpy, quilted surface of sewn blankets.

e. providing a multi-layer surface for integrally woven TPS articleswithout resorting to layering of stacking individual fabric layers.

f. permitting the use of high temperature ceramic yarns such as siliconcarbide to be used in a threadless fabrication method.

The following features of this invention are novel:

a. using the TPS article to provide resistance to high aeroacousticloads after exposure to a radiant heat environment.

b. using a multi-layer weave construction such as angle interlock andlayer-to-layer as a fabric surface capable of resisting highaeroacoustic noise levels.

c. using the integration of multi-layer weave architecture as a facefabric of an integrally woven core structure.

d. using the threadless (no sewing thread to assemble) method tofabricate high temperature high aeroacoustic noise capability TPSarticles.

SUMMARY OF THE INVENTION

The present invention relates to an improved flexible three dimensionalfabric structure comprising:

a multilayer fabric surface for the top face fabric;

a single layer fabric surface for the bottom face fabric surface;

a single layer rib fabric which forms an angled truss configurationconnecting the top face surface and bottom face surface;

a high temperature stable ceramic insulation located between the topface and bottom face and adjacent to the surface of the rib trussfabric,

wherein the top face fabric is woven in an angle interlock mode suchthat the outer top multilayer surface is an integral smooth tightlywoven face sheet such that the rib fabric does not extend to the topsurface, but remains below the exterior surface inter woven with in thefibers of the fabric, and the overall structure has enhanced resistanceto aeroacoustic noise, preferably up to 170 decibels and enhancedresistance to heat, preferably up to 2500° F.

In another embodiment, the present invention relates to an improvedcomposite multilayered flexible blanket insulation comprising a topfabric layer and a bottom fabric layer, high temperature insulationlayer, and optional reflection shield layers and spaces, all securedusing a ceramic thread wherein the top fabric and bottom fabric layersare secured to each other by the ceramic thread at an angle of frombetween about 45 and 135 degrees from the surface of either the top andbottom fabric layer creating triangular prism or trapezoidal prismshaped spaces between the top and bottom fabric and the insulationlocated therewithin has a correspondingly triangular prism ortrapezoidal prism shape within the created spaces, wherein said blanketinsulation is able to withstand an aeroacoustic environment up to about170 decibels and temperatures up to about 2500° F.

In another embodiment, the present invention relates to a method toproduce the improved flexible three dimensional fabric structuredescribed above, which method comprises:

(a) combining during weaving a multilayer top face sheet, a single layerbottom face sheet, and a rib fabric each woven of the same or differenthigh temperature ceramic fiber (or tow) by simultaneous weaving andinterconnection by the rib fabric at locations on the top face sheet andbottom face sheet which are designated as nodes;

(b) warp fibers are woven in a plane at 90° angle to the direction ofthe formed flutes and are filled parallel to the flutes which flutesdefine multiple three-dimensional triangular prism or trapezoidal prismopen volumes;

(c) filling the three-dimensional triangular prism or trapezoidal prismopen volume with insulation comprising heat-resistant ceramic fibers;and

(d) heat cleaning the formed structure at temperatures between about800° F. and 2000° F., which expands the ceramic insulation of step (c)to fill the prism volume and

(e) cooling the structure to ambient conditions.

In another aspect, the present invention relates to a method ofproducing a three dimensional angle interlock ceramic fabric which isstable to high aeroacoustic noise and to high temperatures up to 2500°F., which method comprises:

(a) obtaining multiple separate strands of a ceramic fiber or ceramictow suitable for weaving;

(b) utilizing a modified fly--shuttle loom or a rapier shuttleless loom,which is modified by adding nip rolls to the loom and modification ofthe fabric advancement mechanism, which loom has at least eightharnesses in conjunction with Dobby programming mechanism;

(c) utilizing sufficient heddles for each warp fiber and a suitable reedwhich accommodates about 168 ends per in for a given fabric widthwherein the top fabric has a shuttle, the rib fabric has a separateshuttle and the bottom fabric has a separate shuttle;

(d) drawing fabric warp sheets into the loom through a series oftensioning bars and into each respective harness for each fabric;

(e) utilizing an additional roller system to drive extra length ribfiber into the loom;

(f) translating the warp and fill yarn sequencing in a Dobby patternchain utilizing bar and by indicator wherein each bar represents onefill fiber insertion and each peg indicates the lifting of a specificharness;

(g) weaving the fiber such that the Dobby mechanism reads one patternbar instructing the loom to raise or lower one or more harnessescreating a shed opening;

(h) conveying a shuttle through the shed opening dispensing a fill yarninto its proper location;

(i) locking the fill yarn in place as the harness achieves its highestor lowest position which creates the next shed sequence, concurrentlythe reed pushes back the fill fiber into place and moves to its originalback most position;

(j) utilizing the same shuttle to traverse the created fabric in theopposite direction dispensing another fill yarn in the newly formed shedopening;

(k) repeating steps (g), (h), (i) and (j) as needed to create the threedimensional angular open weave ceramic fabric structure describedhereinabove.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a cross-sectional schematic representation of the threedimensional fabric structure integrally woven fluted truss-core fabricwith an angle interlock outer surface.

FIG. 2 is a cross-sectional schematic representation of an alternativestructure having a layer-to-layer outer surface.

FIG. 3 is a cross sectional schematic representational of the threedimensional fabric structure having the flutes filled with expandedceramic insulation.

FIG. 4 is a cross-sectional schematic representation of the threedimensional fluted core fabric components incorporating the angleinterlock architecture.

FIG. 5 is a cross-sectional schematic representation of individualfabric fiber systems comprising 600-denier silicon carbide fiber.

FIG. 6 is a cross-sectional schematic representation of the woven flutedcore structure with single-play fabrics of the prior art.

FIG. 7 is a cross-sectional schematic representation of the multilayerface sheet having the angle interlock architecture.

FIG. 8 is a cross-sectional schematic representation of an alternativeembodiment showing alternate multilayer face sheet layer-to-layerarchitecture.

FIG. 9A is a cross-sectional schematic representation of the inventionof optimized locking arrangements of rib fabric to outer faces, i.e.,rib lock to angle surface interlock.

FIG. 9B is a cross-sectional schematic representation of the inventionof optimized locking arrangements of rib fabric to outer faces, i.e.,rib lock to layer-to-layer surface.

FIG. 9C is a cross-sectional schematic representation of the inventionof optimized locking arrangements of rib fabric to outer faces, i.e.,optimized locking arrangements of rib fabric to the single ply face.

FIG. 10 is a cross-sectional schematic representation of the dimensionalcharacteristics of fabric structure.

FIG. 11 is a cross-sectional schematic representation of the collapsedstructure and defining the fiber arrangement of the article.

FIG. 12 is a cross-sectional schematic representation of a typicalweaving loom arrangement.

FIG. 13 is a cross-sectional schematic representation of the loomcreating the multilayer fabric.

FIG. 14A is a cross-sectional schematic representation of a single cutinsulation prism (mandrel) before heating.

FIG. 14B upon heating shows the expansion of insulation of FIG. 14A.

FIG. 15 is a cut-away isometric view of the cold insulation insertiontool.

FIG. 16 is a cut-away isometric view of the rigid insulation mandrelhaving the insulation within the insertion tool.

FIG. 17A is a cross-sectional schematic representation of multipleprisms for the cold insulation article.

FIG. 17B shows the expanded insulation after heating the article of FIG.17A.

FIG. 18 is a graphic comparison of silicon carbide TABI cell orientationto air flow at 170 decibels.

FIG. 19 is a graphic representation of aeroacoustic survivability ofNEXTEL AB 312 TABI compared to baseline TABI at 170 decibels.

FIG. 20 is a graphic comparison of the aeroacoustic behavior of flexibleceramic TPS at 170 decibels in the NASA-Ames mini wind tunnel testfacility.

FIG. 21 is a three-dimensional graphic comparison of aeroacousticsurvivability of silicon carbide 600 denier single ply TABI compared tobaseline TABI at 170 decibels.

FIG. 22 is a three-dimensional graphic comparison of aeroacousticsurvivability of layer-to-layer TABI compared to base line TABI at 170decibels.

FIG. 23 is a three-dimensional graphic representation of aeroacousticsurvivability of angle interlock TABI compared to baseline TABI at 170decibels.

FIG. 24 is a cross-sectional schematic representation of the mini-windtunnel test facility (MWTF) used for aeroacoustic and heat measurements.

FIG. 25 is a cross sectional schematic representation of the weaving ofthe bottom face warp fabric.

DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS

Definitions:

As used herein:

"Ceramic" refers to the conventionally known and commercially availableceramic materials of the art which are fabricated in a fiber form.Preferably ceramic refers to silicon carbide, silica, TYRANNO®, alumina,aluminoborosilicate, silicon nitride, silicon boride, siliconboronitride and the like.

"TYRANNO® FIBER" is a registered trademark of the Ube Industric, Led ofTokyo, Japan. It is distributed in the U.S. by the Textron Corporationof Lowell, Mass. 01851. It is a continuous inorganic ceramic fiber madefrom organometallic polymers yielding on heating a ceramic fiber havinga composition of silicon, titanium, carbon and oxygen. It has tensilestrength of 400 KSI, a high modulus, and excellent high temperatureproperties at 2370° F.

One embodiment of the present invention utilizes a 600 denier siliconcarbide yarn to weave a multi-layer top or face fabric whilesimultaneously weaving the rib and bottom fabric and integrallyconnecting these to the multi-layer woven top fabric. The differencehere is that the top face fabric is woven into an angle interlock weaveconstruction which toughens the surface to high aeroacoustic loads whilethe rib and bottom fabrics remain a single-ply fabric. The cores orcells formed are about one inch, triangular in shape and are stuffed andtightly filled with a low thermal conductivity insulative filler such asalumina batting, which has high temperature stability up to about 2800°F.

Referring now to the attached figures, FIG. 1 shows the angle interlockpattern of the present invention which provides a weave architecturewhich has a tougher, tighter fabric surface capable of resisting damageduring exposure to high aeroacoustic loads and eliminating insulationmovement of the insulation filling cores or cells, see FIG. 17B. Thisparticular version has survived 15 min exposure to 170 decibels soundpressure level, after first being exposed to a radiant heat cycle for 2min at 2500° F. The angle interlock fabric is woven to 0.032 inthickness in this case and the overall system density is 10 pounds percubic foot (pcf). The results of aeroacoustic testing comparing theangle-interlock woven surface TPS to a single-ply TABI to the base lineTABI are shown in FIG. 23.

An alternate version of the present invention is also fabricated using600 denier silicon carbide yarn to weave the integrally connectedstructure, but replacing the angle interlock multilayer surface with alayer-to-layer surface weave. This configuration has shown no change toa 10 min exposure of 170 decibels after a radiant heat soak for 2 min at2000° F. These results are shown in FIG. 22. The thermal insulationinserted in the cores was alumina. Another example of above TPS articleuses a low boria content (2%) aluminoborosilicate (ABS) batting as theinsulative filler.

The angle interlock version is also filled with the ABS batting toprovide comparable thermal conductivity and density.

Other ceramic yarns are also employed in place of the silicon carbideyarn depending on the temperature performance requirements. Theseinclude, for example, aluminoborosilicate, silica, TYRANNO®, siliconnitride and the like, as additional examples of other high temperatureyarns for weaving into these complex, integrally connected woven TPSstructures.

Now referring to the figures, the present invention relies heavily uponthe art of weaving, specifically the weaving of integrally woven flutedcore structures. The invention's three-dimensional fabric structure 10is illustrated in FIG. 1. It is significant in that the oppositeparallel face sheets (top face sheet 11 and bottom face sheet 12) andrib fabric 13 which forms the three dimensional truss configuration 10are all integrally connected. The woven preform utilizes a multilayerfiber architecture in top face sheet 11 with single ply constructions inthe bottom sheet 12 and rib fabric 13. The multilayered face 11Aconsists of an angle interlock architecture 14 (at the top) and 15 (atthe bottom). In one embodiment, the invention's structure is wovenentirely with 600-denier silicon carbide fiber. The fine filamentdiameter of this ceramic yarn allows for a high fiber density in thewoven preform. Woven into an angle interlock construction 14, the outermultilayer surface face 11A results in a smooth and tightly woven facesheet, which is an essential characteristic to the invention'saeroacoustic performance. This style of multilayer construction 11 alsoenhances the integrity of the top surface 11A by preventing fibermovement during service loads and temperatures.

As seen in FIG. 2, an alternate multilayered top surface 11A consistingof a layer-to-layer 11 and 11B construction may also be incorporatedinto the invention's top face 11A.

Secondary processing is required to fully establish the thermalprotecting nature of the invention. As seen in FIG. 3 this includesfilling the triangular shaped flutes 16 of the as-woven structure with aceramic insulation 17 followed by a heat cleaning operation to removeall organic binders or finishes. In this heat cleaned, insulatedcondition, the present invention 10A exhibits its flexible ceramic hightemperature characteristics. The fluted core structure of FIG. 1 isunique in that the integrally woven rib fabric structure 13 ensurestotal encapsulation of the insulation 17.

The fluted core fabric structure of the present invention, as shownexpanded in FIG. 4 consists of three individual fabrics, two outerparallel face sheets 1t and 12 and one rib fabric 13. In one embodiment,each fabric is woven from silicon carbide fiber having 600-denier. Thesethree fabrics are woven simultaneously and interconnected by the ribfabric 13 at locations designated as locks or nodes 14 and 15. Warpfibers are woven normal to the direction of the flutes, and fillparallel to the unfilled flutes 16.

In other embodiments the top surface fabric 11, bottom surface fabric 12and rib fabric 13 are each independently selected from the same or adifferent ceramic fiber. For example, top surface fabric is a hightemperature fiber, such as TYRANNO®. This outer surface 11A is incontact with the environment and therefore must withstand the highesttemperatures and most severe acoustic (and mechanical) stress. Thebottom fabric 12 and rib fabric 13 are selected from ceramic fiberswhich are less expensive, easier to fabricate, have a lower meltingpoint, etc. (than the top fabric 11), because they are not subjected tothe high temperatures and mechanical or aeroacoustic pressures. Forexample, a TYRANNO® fiber (defined above) or silica is used for the topface surface, and lower temperature fiber silicon carbide is used forthe rib and bottom fabric. The invention's fluted core structureincludes design parameters, such as yarn system, fabrics' weave style,fabric ply thicknesses, and flute height.

Each of the three fabrics contains its own warp and fill fiber system(see FIG. 5), with the exception of the nodes. There, several fillfibers are shared by the rib and opposite faces to create the locks.Each fabric comprising the structure requires its own design, and theoverall structure design must be coordinated so that the warp yarns ofthe rib fabric 13 interlock properly at the nodes 14 and 15 formed withthe face fabrics 11 and 12.

In ordinary woven fluted core structures 10, the individual fabricsusually are single ply with a plain weave construction, see FIG. 6.However, the present invention incorporates a multilayered fiberarchitecture in the outer face, containing four warp layers 20, 21 22and 23 and three fill layers 24, 25 and 26, see FIG. 7. Referred to asangle interlock (e.g. 11) or through the thickness weaving, it is formedwhen continuous warp fibers weave uninterruptedly along an angled path,through all three fill layers comprising the fabric's thickness to theinner surface, and return to the outer face to complete one weave cycleor repeat.

As an alternate surface construction, FIG. 8 demonstrates that theinvention may instead use a layer-to-layer architecture rather than theangle interlock. In this weave, the warp fibers (33-40) weave normal(90°) to the three fill layers 41, 42, 43, but do not pass through theentire thickness.

FIG. 9A is cross-sectional schematic representation of the fabricstructure having an optomized locking arrangement of rib fabric 13 tothe outer face 11A of fabric 11.

FIG. 9B is also a cross-sectional schematic representation of the fabricstructure having rib fabric 13 to outer face fabric 11A having a riblock for the layer-to-layer top surface shown as 11B.

In FIG. 9c, the opposite (or bottom) face and rib fabric 13 are bothsingle ply, plain weave construction. The locking arrangements 14 and 15of the rib fabric 13 to the multilayered and single ply faces 12 areoptimized to offer the greatest mechanical integrity.

FIGS. 10 and 11, show in a preferred embodiment, a pair of rib warpfibers making up the rib fabric are programmed to intersect theunderside of the multilayer fabric and weave through two fill layerthicknesses. The rib fibers 30 and 31 pass over three fill fibers of themid fill layer and four of the bottom layer, and then exit themultilayer fabric after which, they resume interlacing with fill fibersto form the rib fabric 13. The connection of rib fabric 13 to outer face11A also forms the triangular shaped unfilled flutes 16 of approximatelyequally dimensioned legs, with angles between legs of about 60°, and theinner flute height of the structure measuring about 1.0 in. Theadditional fabric thicknesses of the multilayered top fabric 11 (0.030in) and single-ply lower fabric 12 (0.009 in) results in an overallpanel thickness of 1.03 in. The present invention utilizes 600 deniersilicon carbide fiber throughout the preform structure. Based upon thefiber's cross-sectional area and desired characteristics of the wovenstructure, warp and fill counts are established for the multilayeredsurface, single ply face and rib.

FIG. 11 is a schematic representation of the collapsed structure 10A ofthe unfilled TABI woven article. FIG. 1 shows the stretched unfilledTABI structure 10.

Table 1 below summarizes the fiber counts for one embodiment of thepresent invention's woven structure.

                  TABLE 1    ______________________________________    FLUTED CORE FIBER COUNTS    Multilayer Fiber    Top       Rib   Bottom    Architecture               System   Face      Fabric                                        Face    ______________________________________    Angle      Warp     112.0     28.0  28.0               (yarn/in)    Interlock  Fill     84.0      26.5  30.0               (yarn/in)    ______________________________________

Given the attainable fiber counts and desired flute dimensions, thenumber of fill yarns contained within each section of the preform may becalculated. For example, based on a fill fiber count of 26.5 yarn/in forthe rib fabric, 1.0-in flute height, and about a 60° between rib andouter face, a total of 30-fill fibers are required in the rib fabricbetween nodes. Following similar calculations for other fabric sections,a design schematic of the invention's structure may be developed, seeFIGS. 1-11. Every warp and fill yarn is arranged to produce the desiredconstruction and flute dimension. The structure is then illustrated in acollapsed form, see FIG. 11, from which each warp fiber system (seeFIGS. 1-8) can be identified, as well as each fill yarn system making upone design repeat of the structure. The fiber arrangement defines thesequence in which warp yarns are programmed to weave around insertedfill yarns. The numbered warp fibers correspond to the loom harness thatcontrols the raising or lowering of that warp fiber group at a specificfill (pick) number. This information is basic and sufficient to enableone of skill in this art in developing the loom programming.

Programming, Loom Preparation and Weaving:

The present invention's structure is woven on a modified Cotton-Kingfly-shuttle loom from Crompton & Knowles, adapted with a Dobbyprogramming mechanism from Draper or Staubli. The loom contains eightharnesses, one controlling each warp sheet, with sufficient heddles foreach warp fiber, and a suitable reed that will accommodate 168 ends/infor a given fabric width. A typical loom set-up to weave the fluted corestructure is shown schematically in FIG. 12. Each of the fabric warpsheets is drawn into the loom through a series of tensioning bars andthen into their appropriate harness. Since rib warp yarns weave a longerpath than those from the parallel faces in a given unit length, anadditional roller system (nip rolls) must be incorporated to drive extralength fiber into the loom. The warp and fill yarn sequencing, FIGS. 12and 13, is translated into a Dobby pattern chain made up of bars and pegindicators; each bar representing one fill insertion and each pegindicating the lifting of a particular harness. This programmingprovides the proper sequencing of shed openings for each fill yarninsertion. During weaving, the Dobby mechanism reads one pattern barinstructing the loom to raise or lower one or more harnesses (warpsheets). This forms a shed opening through which a shuttle is thenpowered, dispensing a fill yarn as it traverses the width of fabric. Onthe subsequent pattern bar, a different set of harnesses will be raisedor lowered. Simultaneously, the graduated reed 40 moves forward andbeats (packs) the just-inserted fill yarn into its proper location, andis immediately locked into place as the harnesses reach their highest orlowest movement. FIG. 13 illustrates a fill insertion in themultilayered face sheet. Here seven warp sheets 21, 22, 23, 31, 30, 27,28, are shown lowered by their harness--while one warp 20 remainsraised. A shuttle dispenses a fill yarn 50 into the shed opening 51. Asharnesses--are raised and lowered for the next shed sequence, reed 40beats the fill fiber into place and rocks to its back most position. Thesame shuttle traverses across the fabric in the opposite directiondispensing another fill yarn in the newly formed shed. Each of the threefabrics in the invention's structure requires its own shuttle.

With each fill yarn insertion there follows an advancement of theas-woven fabric by the loom's gear driven cloth roll. A combination ofgears and ratchets determines the proper fill density in each of thefabrics comprising the fluted core structure. A pawl/ratchet system alsoadvances the required length of rib warp fiber through the nip rollers.

The flexible three dimensional ceramic fabric structure is also producedusing the description provided herein under contract by BP Chemicals(Hitco), Inc., Advanced Materials Division Fibers and Materials, 1600West 135th Street, Gardena, Calif. 90249. Other commercial companieswhich can produce the ceramic woven article (with this specification)include, for example, Mutual Industries, Philadelphia, Pa., TextileTechnologies, Inc., (TTI), Philadelphia, Pa., or Textile Products, Inc.,Anaheim, Calif.

Insulation Processing:

Subsequent to weaving of the invention's structure, the fluted cells 16are filled with a rigidized ceramic insulation 17A, see FIG. 14. Theentire structure is heat cleaned to remove all organic binders, duringwhich time the insulation expands to fill the flutes tightly andcompletely 17. In this insulated, heat-cleaned state, the inventionacquires its flexible thermal protection characteristics with optimizedresistance to high aeroacoustic noise.

The ceramic insulation 17 usually consists of high purity alumina fibers(95% Al₂ O₃, 5% SiO₂) that are combined in a mat form to yield a 6-lb/cuft density at a 1.0-in nominal thickness after heat cleaning. Theinsulation sheets are usually supplied as prerigidized boards using anorganic binder, and having a measured thickness less than the innerflute height dimension. In rigid form, the insulation panels are cutinto mandrels approximating the flute shape and dimension, and theneasily inserted into the hollow cores. The rigid insulation boards areof any length suitable for handling and formation, but the width mustequal the flute length.

An ordinary table saw capable of adjustable angled cuts is used toproduce the triangular shaped ceramic insulation mandrels. Sincethe-insulation mandrels will expand only in its thickness direction (orflute direction), mandrels must be cut to the dimensions of the flute'stop and bottom bases, see FIG. 14. The angled cut depends upon theactual supplied insulation board thickness. When cut properly, theinsulation expands to the shape of the flute cross section and maintainits 6-pcf density.

The process to fill the fabric flutes with the rigid insulation mandrelsis facilitated by an insertion tool 62. The tool consists of a 0.004 inpolyester film 61 formed to the triangular flute shape and attached tothe end of an inspection mandrel 62. See FIG. 15. The inspectionmandrels 60 constructed to the exact shape and dimensions of thefabric's cells, are used to verify the flute size.

The insulation mandrels are enveloped in the polyester shroud 61, FIG.16, and the tool 60 is pulled through the flute 16. The polyester film61 eliminates the abrasion and friction between the woven fabric andinsulation mandrel 17A that results if it is not otherwise used. Whenthe insulation 17A mandrel occupies the entire flute length, theinsulation is held in place and the insertion tool 60 is extracted.

In FIG. 17, adjacent flutes 16 are similarly filled with insulationmandrels 17A to form a length of an insulated panel structure 65. Brokenor discontinuous insulation mandrels which may create undesirable heatpaths are removed from the flutes and replaced with a whole mandrel.Once a panel structure has been insulated with rigidized ceramicmandrels, the structure 65 is subjected to a heat-cleaning operation ina gas-fire, air circulating oven. The heat-clean cycle is defined asabout 4 hr at 850° F. Any organic binders such as yarn finishes, orrigidizing binders contained in the insulation are entirely removed. Theceramic insulation exhibits its resilient nature and expands fullyinside the fabric flutes attaining the 6-PCF density.

The structure of the present invention can be of any size or volume.However, when used in aerospace applications, size and pounds per cubicfoot considerations are important. Therefore, the structure can be ofany useful length and width. The thickness, when the volume between thetop face sheet and bottom face sheet is filled with ceramic insulation,is between about 0.5 and 6 in, preferably between about 0.5 and 3 in,and especially preferred is about 1 in.

FIG. 18 is a two dimensional graphic representation comparing a siliconcarbide TABI cell based on the orientation to air flow at 170 dB. As canbe seen a test at 2000° F. for two min shows that the baseline 1800 desingle ply, angle interlock and layer-to-layer construction exhibitcomparatively minor damage. On the other hand, the test at 2500° F. fortwo min shows that the angle interlock structure of the presentinvention is clearly superior and suffers little damage.

FIG. 19 is an isometric graphic representation of the aeroacousticsurvivability of NEXTEL AB312 TABI compared to baseline TABI at 170 dB.As can be seen the tests at 1440° F. for 10 min and at 2000° F. for twomin have roughly comparable minor damage. However, at 2500° F. for twomin, severe damage occurs to the structure causing loss of insulationvalue.

FIG. 20 is a graphic comparison of the aeroacoustic behavior in a miniwind tunnel test (see FIG. 24) of flexible ceramic TPS at 170 dB atvarious temperatures. As is seen, at 2500° F. there is significantdamage to the uncoated AFRSI and the C-9 coated AFRSI.

FIG. 21 is a graphic representation of the survivability of SiC 600 deTABI as compared to baseline TABI at 170 dB. As can be seen, at 2000° F.for 2-min, the baseline TABI survives with little or no damage. The SiC600 de for parallel and perpendicular flow degrades and the insulationvalue is lost. At 2500° F. for two minutes, the structure of all samplesdegrade to a point that the insulation is lost.

FIG. 22 is a graphic representation of aeroacoustic survivability oflayer-to-layer TABI as compared to baseline TABI at 170 dB. As can beseen at 2000° F for two min, only minor or no damage occurs. However, at2500° F. for two min, in all samples severe degradation occurs andinsulation is lost.

FIG. 23 is a graphic representation of the aerocoustic survivability ofangle interlock TABI of the present invention as compared to baselineTABI at 170 dB. As is seen in the tests at 2000° F. for 2 min, there islittle or slight degradation to any of the samples. However, when thesamples are heated at 2500° F. for two min, the angle interlock TABI ofthe present invention survives with little or no degradation. Thebaseline TABI under these conditions in severely degraded and theinsulation value is lost.

The following Examples are presented for the purpose of explaining anddescribing the present invention. They are not to be construed to belimiting in any way.

EXAMPLE 1 WEAVING OF THE ANGLE INTERLOCK FRAMEWORK

The fiber counts of the angle interlock face sheet (112 EPI×29 PPI) andthe single ply bottom face (28 EPI×33 PPI) were established. The rayonserved 600-denier SiC warp was entered into the loom. These fiberscomprised the TABI sheets and the rib structure.

The node locks connect the rib fabric to the top and bottom faces.Several alternative node designs for both faces had been developed.Style B (FIG. 9A) and Type A (FIG. 9C) designs were selected as locksfor the top and bottom faces respectively. In the Style B lock, the ribfabric is connected to the angle interlock face as the rib warp passesover two of the three fill layers in the angle interlock fabric. Thisdesign was chosen over Style A since it locked to one additional layer,offering greater locking strength. Originally Style C appeared to be atighter lock with the interweaving of the rib warp to a single fill yarnin the second layer of the angle interlock face. There was a question asto whether this tightness would result in weaving difficulties. Theinterweaving of the rib warp might restrict the close packing of thefill fibers and create a gap in the node center of the outer layer.Also, there was a possibility of the rib fibers shearing due to thefiber density and severe crimping during beat-up. Therefore, Style B(FIG. 9A) was chosen.

In earlier SiC TABI structures, (see FIG. 9) the Type A node design wassuccessfully used to lock the rib fabric to the single layer facesheets. The Style A node permits a more secure lock with greaterintegrity over Styles B and C. This is true using the finer 600-denierSiC fiber. Node design Style A was selected as a preferred embodiment.

The correct flute size could be established by adjusting the lengths ofthe rib and face fabrics. The node locks selected were incorporated intothe TABI fabric design and included in the loom programming. Severallocks of both Style B and Style A were successfully woven at theestablished fiber counts without difficulties. Samples of each were cutfrom the loom, heat-cleaned and examined for fiber breakage and lockintegrity. The SiC fibers in each lock survived the weaving withoutdamage and the locks appeared tightly woven exhibiting toughness andstrength.

Some warp fiber floats occurred in the bottom face during weaving, seeFIG. 25. Random SiC fibers 101 and 102 from the bottom face weremalfunctioning (hanging-up) as a result of tensioning weights 103, 104,105 and 106 not acting properly on the fiber about rollers 107 and 108.The tensioning weights were too long and would ride on fibers belowthem. Without the taughtness in the fiber, floats occur. Shortertensioning weights 109, 110, 111 and 112 were substituted which actedmore positively, taking up any fiber slack produced during the weavingoperation and about rollers 115 and 116. This change eliminated anyfurther floats in the bottom face.

The target TABI dimensions for this debugging task are defined in FIG.10. The TABI fabric incorporating an angle interlock face sheet wasexamined. This operation included adjusting the flute dimension andgeometry, correcting any defects in the loom programming, weaving trialsamples, and fine tuning the loom functions.

The initial fabric woven to evaluate the node locks was also used forthe first check of the TABI flute cell size. A section of this fabricwas cut from the loom, heat-cleaned, and inspected for cell dimensionand defects. Upon inspection, the heat-cleaned sample first revealed arepetitive weave defect (appearing as a line) across the angle interlockface sheet. Also noticeable were randomly broken warp fibers in thebottom face. This breakage was attributed to the fiber beat-up requiredto obtain the high fill count (total) in the entire TABI structure. Whenweaving the individual fabric samples for the opposite faces, the ribfibers were programmed to float between the two, so the bottom facesheet did not experience this severe beat-up and was woven withoutbreakage. With the addition of the rib fabric and locking nodes, thefill density increased amply to cause higher beat-up resulting in thebreakage of warp fibers in the bottom face fabric. It was necessary toreduce the fill count to 30 PPI in tie bottom face to avoid furtherbreakage.

The rib fabric was measured at approximately 1.31 in creating anoversized cell. To adjust the cell size it was required to build anentirely new program chain. The revised programming involved the removalof several picks from the rib fabric which would effectively weave ashorter rib. The fill count in the bottom face was also adjusted by thisprogram change.

A 600-denier SiC fiber was woven into an integrally woven fluted corewith an angle interlock face sheet.

After installing the new weave program on the loom, a second TABIstart-up sample was produced, approximately two feet long. A section wascut from the loom, and again heat-cleaned and inspected. Similar to thefirst sample, a defect line occurred across the width of the angleinterlock face sheet. While examining the program, it was discoveredthat a small peg, which indicates the lifting of a harness wasimproperly placed. The bottom face sheet did not experience any furtherbreakage after the reduction in its fill count. A portion of theheat-cleaned sample was sliced open to attain a measurement for the ribfabric length, and to examine the inside walls of the flute and innerlock formation. The rib fabric measured 1.20 in exceeding the targetvalue of 1.14 in. It was again necessary to reduce the rib length byremoving picks from the connecting web. The rib fabric appeared intact,as well as the top and bottom locks.

The flute geometry of this sample and an accurate measurement of theoverall panel thickness were observed by filling a small section withSaffil insulation and heat-cleaning at 850° F. Rigid Saffil insulationmandrels were cut to the dimensions shown in using an ordinary tablesaw, and inserted into the fabric flutes (see FIGS. 14A, 14B, 15 and16). These dimensions consider the spring-back nature of the insulationafter binder removal, and that the Saffil must fill, the entire cell andmaintain 6 PCF density at the designed cell height. The overall panelthickness of the heat-cleaned TABI sample was then measured under 3.4psi, at 1.08 in (from top node to bottom face fabric), surpassing thetarget of 1.03 in. The triangular flute configurations were distorted bya length of the excess rib fabric. Saffil insulation filled the flutestightly, actually forcing the single ply bottom face to bulge slightlyfrom a flat configuration between the locking nodes.

The TABI fabric design required a final modification to adjust the ribfabric length and obtain the desired panel thickness. The reduction inrib length was completed first by removing a pair of picks from the rib,and secondly, by adjusting the drive let-off for the rib warp. This ribdrive system consists of a pair of drive rollers controlled by a ratchetgear which allows for slight adjustments to the rib length. The rib warpfibers pass through these drive rollers into the loom, and ratchet gearsare selected for the desired amount of rib advancement.

About three feet of SiC TABI fabric was woven using the modifiedprogramming and the rib drive gear adjustments. A section of fabric wascut from the loom for inspection of the rib length, cell dimension,flute geometry, and any weaving defects which may have occurred. Aheat-cleaned sample of this fabric revealed a rib fabric length of 1.14in, indicating adjustments were properly made inner surface locks,appeared undamaged by the weaving and in good condition. The remainingas-woven section was insulated with Saffil mandrels and heat-cleanedaccordingly. The overall panel thickness of the TABI sample measured1.02 in, and it exhibited a uniform cross section of tightly filledflutes, with straight ribs. As in previous samples, the bottom faceprotruded between the locking nodes due to the resilieney of the Saffilinsulation. The angle interlock top face appeared flat with a uniformweave pattern. The sample was free of weaving defects and anomalies.

The final dimensions and schematic of the 600-denier SiC triangularfluted Core TABI fabric incorporating an angle interlock face sheet areshown in FIG. 11.

An initial four foot TABI panel was produced. Few difficulties wereencountered during the weaving operation of this panel, except foroccasional breakage of the SiC warp fibers. Once woven, the TABI fabricpanel was cut from the loom, visually examined for weaving defects, andflute size inspected with check mandrels. Prior to heat cleaning,defects can be masked by the rayon serve; however, careful inspection ofthe panel did not reveal any major flaws. Inspection mandrels were usedto check each individual cell in the panel. The TABI panel containeduniform and properly sized flutes with the exception of two undersizedcells. After inspection of the flutes, saffil insulation mandrels werecut as described above and inserted into the TABI fabric. The undersizedflutes were custom fit with smaller Saffil mandrels. The insulationprocess makes use of a specially fabricated insertion tool consisting ofa 0.004-in (MYLAR®) sheet attached around the perimeter of an undersizedtriangular check mandrel. A Saffil mandrel is placed inside the MYLARenvelope helding it firmly with a small gap between the check mandrelend. The check mandrel is then inserted into the fabric and pulledthrough the entire cell length until the insulation mandrel wascompletely inside the flute. Placing a straight edge in the separationbetween the mandrel and insulation would allow the insertion tool to bewithdrawn from the fabric, while the Saffil insulation remained in thecell. This insertion tool facilitated the insulation process and alsominimized the breakage of insulation mandrels.

The insulated TABI panel was then heat-cleaned in a gas fired oven forfour hours at 850° F. to remove all organic binders, sizing, and rayonserving. Upon examination of the heat-cleaned panel, angle interlock topface sheet protruded between the locking nodes (bump-like appearance).The protrusions only occurred over a 18-20 inch area in the center ofthe panel. They were not evident at the ends of the panel where thepanel appeared flat. It was not known what caused the bumpiness orwhether this effect might reappear on subsequent panels. It should alsobe noted that this characteristic was not noticeable prior to heatcleaning nor obvious in preceding start-up samples. Although the topface distorted at the panel's center, the flute geometry maintained itsuniformity, and the Saffil insulation filled the flutes tightly.

Test specimens cut from the panel were used to determine the panelthickness, fabric areal weight, TABI areal weight, and TABI density. Theactual TABI characteristics and estimated values are compared in TableA. The panel thickness measured 1.02 in. The actual areal weight of heatcleaned TABI fabric (without insulation) weighed 29.65 oz/sq yd, within4% of the estimated weight based on target fiber counts. The TABIdensity measured 9.93 lb/cu ft, higher that the calculated density of8.21 lb/cu ft which is based on 6.0 lb/cu ft insulation density at 1.0in. The difference in these values can be attributed to the actualnominal density of the Saffil insulation of 7.5 lb/cu ft.

                  TABLE A    ______________________________________    TABI Characteristics    TABI Fabric   TABI Panel    Areal         Areal       TABI    TABI Panel    Weight, H/C   Weight, H/C Density Thickness    (oz/yd.sup.2) (oz/yd.sup.2)                              (lb/ft.sup.3)                                      (in)    ______________________________________    Estimated            22.48     100.48      8.21  1.03    Actual  29.65     121.60      9.93  1.02    ______________________________________

Weaving continues after removing the first panel from the loom. Thedistance the fabric must travel through the loom drive and idler rollersbefore reaching the take-up roll, where fabric is removed, is nearly 3.5ft. In order to cut a 4.0 ft panel from the loom a total of 7.5 ft mustbe woven. At the time of doffing panel 1, the second TABI panel wascomplete and the third partially woven. Without evidence of defects orprotrusion-effect on the as-woven panel 1, it was decided to completepanel 3, begin panel 4, and then doff both panels 2 and 3 together. Itwas not until midway through the completion of panel 4 that the surfaceeffect was discovered on the first panel. Any changes of modificationsto the weaving at this point might jeopardize the physicalcharacteristics of the fourth panel. Also, the protrusions in the firstpanel might have been inherent to that panel only and so the weaving ofpanel 4 continued. When removing panels 2 and 3 from the loom, panel 3was mistakenly cut short by 0.5 ft. This difference was made up byincreasing the length of panel 5 accordingly.

TABI panels 2 and 3 contained only two and three undersized cellsrespectively, each being fit with custom sized Saffil mandrels. Allother flutes were filled with properly cut Saffil insulation mandrelsaccording to the insertion process described above. Both panels wereheat-cleaned simultaneously and then inspected for major defects. Theprotrusions encountered in panel 1 reappeared in both 2 and 3 panels butto a lesser degree. Few random fiber floats occurred in the bottom faceof both panels, due primarily to broken rayon serving being entangledwith adjacent fibers. Cross-sections of the insulation filled flutesappeared uniform.

After discovering the protruding effect of the angle interlock top facein panels 2 and 3, production of TABI fabric was interrupted todetermine a course of corrective action. However, at this time theweaving of panel 4 was complete, and weaving had commenced on panel 5.

During the completion of panel 6, panel 4 was cut from the loom. Thepanel was processed similarly to the proceeding three panels: fluteinspection, insulating, heat-cleaning, and final inspecting. The TABIfabric flute dimensions were correct and uniform throughout the panel.The cells were insulated with pre-cut Saffil mandrels and the panelheat-cleaned. The flutes were filled tightly with the Saffil insulationdiaplaying, a consistent, flute geometry. The panel exhibited bumpsagain on the angle interlock top face, only in the center portion of thepanel while the adjacent edges appeared flat.

The angle interlock face sheet weaves above the rib fabric and bottomface, and forms the outer fabric as it passes over the front idler roll81, FIGS. 12 and 13. At this roll, it has not yet reached a completelycollapsed state and has an appreciable thickness, unlike the conditionat the pin-roll where the fabric is much flatter. Combining thethickness of each fabric indicates that the outer angle interlock layersare further from the center of the idler roll (R_(ir) +t_(t) +t_(r)+t_(b)) than the rib and bottom face (essentially R), creating a cameffect (FIG. 12). During each take-up advance of the fabric, the topface is pulled an incremental distance more than the other two fabricscausing the top face to be a percentage longer. This in effect weavesthe TABI fabric on a curvature. At the time, an idler roll 81, FIG. 12of 6.38 inch diameter was being used. By adding the thickness to theidler roll, a 2.0% increase in length along the outer surface isattained. Translated into linear length, the top face sheet of a 48 inchpanel may actually be nearly 49.0 inches. When in a flat position, theexcess top face fabric would be more pronounced in the center(protrusions), and less at the ends where there is relief from the cutedges (flat). Minimizing the cam effect could be achieved by reducingthe idler roll diameter. The existing idler was replaced with one of2.30 inch, and panel 6 was woven. No other changes were made to the loomset-up or weave design.

Both panels 5 and 6 were removed from the loom and further processed.After heat-cleaning, the panels were compared for flatness across thetop face. The surface of the angle interlock fabric had improved greatlyin panel 6 suggesting that the combination of the large diameter idlerroll and the fabric thickness stack contributed to theprotrusion-effect. The panel appears uniformly flatter along the length,though a few pairs of cells did contain protrusions less severe thanthose seen in panels 2, 3, or 4.

Invention's Physical Characteristics:

In its final heat-cleaned insulated condition, the flexible ceramicthermal protection system exhibits the following physicalcharacteristics:

                  TABLE 2    ______________________________________    ANGLE INTERLOCK PHYSICAL CHARACTERISTICS    HEAT-CLEANED, INSULATED CONDITION                Top          Rib     Bottom    Fiber Counts                Face         Fabric  Face    ______________________________________    Warp (yd/in)                112.0        28.0    28.0    Fill (yd/in)                84.0         26.5    30.0    Fabric Thickness                0.030        0.009   0.010    (in)    ______________________________________    Overall Panel Thickness                      1.03    (in)    Structure Areal Weight                      121.60    (oz/yd.sup.2)    Structure Density 9.84    (lb/ft.sup.3)    ______________________________________

The insulation structure also demonstrates sufficient flexibility toconform to contoured curvatures.

EXPERIMENTAL TEST CONDITIONS

Radiant Heat Exposure Test--A 1 atm Radiant Lamp Test Apparatus asreported in Reference 11 was used to precondition all test articles. Theprimary purpose of this procedure was to expose the surface fabric ofthe different TPS constructions to a surface conditioning temperatureprior to any acoustic exposure. Various temperatures and times wereused. Temperatures of 1200° F., 2000° F., and 2500° F. were useddepending on the particular ceramic fabric. Exposure times were 10 minat 1200° F., 2 min at 2000° F. and 2 min at 2500° F. All the testarticles were cooled to room temperature (about 20° C.) beforeremounting into the aeroacoustic test configuration. Also the samplesize (6.5 in by 7.5 in long by 1.0 in deep) was the same for both theradiant heat test and the mini-wind tunnel test facility which minimizedhandling and mounting damage to the ceramic blankets being evaluated.

Mini-Wind Tunnel Test Facility (MWTF)--Aero-acoustic testing wasconducted in a small wind tunnel test apparatus specifically designed tosimulate oscillating air loads on the surface of the AFRSI or TABIarticles. A full description of the design, operational and performancecharacteristics are detailed in the C. F. Coe references cited above.

This MWTF provided the advantage of small sample size, rapid start orstop capability, constant visual observation, and excellent control ofaerodynamic conditions. For this study, all test articles were exposedto a dynamic pressure of 510 lb per sq ft, total pressure setting of 6psi, a fluctuating pressure of 2.7 psi, and an overall sound pressurelevel of 170 decibels. The surface area exposed to this condition was3.5 in by 5 in. Typically, the TABI test panels had three complete coresexposed to this environment in the parallel direction and at least fourcomplete cores tested in perpendicular flow direction. Also, a rotorspeed of 100 revolutions per sec was selected because of the superiorwaveform and amplitude measured at this condition. Prior to insertion ofthe test article into the MWTF, a calibration panel was inserted intothe test section to simulate the entry-like aerodynamic conditionsindicated. A schematic of the MWTF is represented in FIG. 24.

Table 3 lists the integrally-woven core blanket insulation of thepresent invention.

Table 4 provides additional measurements for the surface weave geometryof the structure of the present invention.

                  TABLE 3    ______________________________________    FLEXIBLE CERAMIC TPS CONSTRUCTION    Sewn, Ouilted    Blanket   OML Fabric OML Thread Insulation                                           Coating    ______________________________________    Uncoated  Silica     Silica     Silica None    AFRSI    Coated AFRSI              Silica     Silica     Silica C-9                                           Coating    ______________________________________    Integrally                      Face    Woven Core                      Fabric    Blanket   Yarn       Insulation Style    ______________________________________    TABI-1800 SP              1800 de    Silica     Single-Ply              Silicon               Plain              Carbide               Weave    TABI-600 Al              600 de Silicon                         Alumina    Angle-              Carbide               Interlock    TABI-600 LL              600 de Silicon                         Alumina    Layer-to-              Carbide               Layer    ______________________________________

                  TABLE 4    ______________________________________    SURFACE WEAVE GEOMETRY OF TOP FACE FABRIC              Face    Fiber       Fabric   Yarn Density            Diam-   Thick-               Fila- Crimp            eter    ness,    Warp, Fill, ments/                                               Factor,    TABI    μm   in.      epi   ppi   Strand                                               %    ______________________________________    1800    15      0.0107   16.0  24.0  500   8    de SiC,    Single    Ply    600     12      0.009    28.0  29.0  250   3.5    de SiC,    Single    Ply    600     12.     0.032    112.0 83.5  250   9.5    de SiC,    Angle    Interlock    600     12      .029     112.0 61.5  250   7.5    de SiC,    Layer-to-    Layer    ______________________________________

While only a few embodiments of the invention have been shown anddescribed herein, it will become apparent to those skilled in the artthat various modifications and changes can be made in the fabrication ofa flexible ceramic thermal protection system having an angle interlockconstruction which is resistant to high aeroacoustic noise and at hightemperatures without departing from the spirit and scope of the presentinvention. All such modifications and changes coming within the scope ofthe appended claims are intended to be carried out thereby.

We claim:
 1. A method of producing a three dimensional angle interlockceramic fabric structure which is stable to high aeroacoustic noise ofabout 170 decibels and to high temperatures up to about 2500° F., whichmethod comprises:(a) obtaining multiple separate strands of a ceramicfiber or ceramic tow suitable for weaving having multiple warp fibersand multiple fill fibers; (b) utilizing a modified fly-shuttle loom or arapier shuttleless loom which has nip rolls, a modified fabricadvancement mechanism, and at least eight harnesses in conjunction witha Dobby pattern chain; (c) utilizing sufficient heddles for each warpfiber and a reed which accommodates about 168 ends per inch for a givenfabric width wherein a multilayered top fabric, rib fabric, and a singlelayered bottom fabric are each woven of high temperature ceramic fiberswith a separate shuttle; (d) drawing the warp sheets into the loomthrough a series of tensioning bars and into each respective harness foreach fabric; (e) utilizing an additional roller system to drive extralength of a rib fiber into the loom; (f) translating a warp and fillfiber sequence into a Dobby pattern chain which chain utilizes bars andpegs wherein each bar represents one fill fiber insertion and each pegindicates a lifting of a specific harness; (g) weaving the fiber in aparticular direction such that the Dobby mechanism reads one pattern barinstructing the loom to raise or lower one or more harnesses creating ashed opening; (h) conveying a shuttle through the shed opening anddispensing a fill yarn in one direction into a specific location; (i)locking the fill yarn in place as the harness achieves its highest orlowest position which creates the next shed sequence, concurrently thereed pushes back the fill fiber into place and moves to its originalback most position; (j) utilizing the same shuttle to traverse thecreated fabric in a direction which is opposite to the direction in step(h) dispensing another fill yarn in the newly formed shed opening; (k)interconnecting said rib fabric at locations on said top and bottomfibers designated as nodes; (l) repeating steps (g), (h), (i), (j) and(k) as needed to create three dimensional angular triangular prism ortrapezoidal prism volumes defined by flutes formed at a 90° angle to thedirection of the fiber weaving; (m) filling said three-dimensional prismvolume with insulation of heat resistant ceramic fibers to create aformed structure; and (n) cleaning said formed structure at temperaturesbetween about 800° F. and 2000° F.
 2. The method of claim 1 wherein saidinterconnecting of said rib fabric is at an angle of between about 40and 80 degrees or about 110 to 140 degrees from the top fabric andbottom fabric.
 3. The method of claim 2 wherein said interconnecting ofsaid rib fabric is at an angle between about 40 and 65 degrees or about115 to 140 degrees.
 4. The method of claim 1 wherein said filling ofsaid volume is with high temperature ceramic insulation selected fromsilica, alumina, aluminoborosilicate, silicon carbide, silicon nitride,silicon boride, silicon-titanium-carbon-oxygen, or silicon boronitride.5. The method of claim 1 wherein said filling step creates a formedstructure which is also stable to an oscillating pressure of about 3psi.
 6. The method of claim 1 wherein said weaving step further createsa distance between said top and bottom fabrics between about 0.5 and 3in.